1. Field of the Invention
The present invention relates to a non-aqueous secondary battery, and more particularly to a high voltage secondary battery in which a lithium/cobalt/antimony oxide is used as a positive electrode active material, whereby charge and discharge capacity is improved.
2. Description of the Related Art
With the miniaturization and power economization of electric devices and the like, secondary batteries using alkali metal such as lithium have been put into practical use. In the case where alkali metal alone such as lithium is used as a negative electrode, the following problems arise: Due to the repetition of charge and discharge cycles, i.e., the dissolution-deposition process of the alkali metal, the alkali metal deposits on an electrode surface to generate dendrites thereon. When the dendrites grow, they penetrate a separator in a battery to come into contact with a positive electrode, causing a short-circuit in the battery.
In order to overcome the above-mentioned problem, it is known that an alloy of alkali metal is used as a negative electrode in a secondary battery instead of alkali metal alone. In this case, the generation of dendrites can be decreased, compared with the case in which the alkali metal alone is used as a negative electrode, thereby improving charge and discharge cycle characteristics. However, the use of an alloy cannot completely prevent the generation of dendrites, and in some cases, a short-circuit is caused in a battery. In recent years, a battery having a negative electrode which uses an organic material such as carbon or a conductive polymer which inserts and deserts alkali metal ions, instead of the conventional electrode materials such as alkali metal or its alloy which utilizes a dissolution-deposition process or dissolution-deposition-diffusion-in-solid process, has been developed. As a result, the generation of dendrites caused in the case where alkali metal or its alloy is used can be prevented, whereby the problem of getting a short-circuit in the battery is substantially overcome.
On the other hand, as a positive electrode of a non-aqueous secondary battery, utilization of V.sub.2 O.sub.5, TiS.sub.2, WO.sub.3, MnO.sub.2, and the like had been attempted. However, these substances have a low discharge voltage of 2 to 3 V. In general, LiCoO.sub.2 having a high discharge voltage is used (e.g., see Japanese Laid-Open Patent Publication No. 55-136131).
For example, K. Mizushima et al., Mat. Res. Bull., 15, p. 783-789, (1980) shows a battery prepared by the following process. First, lithium carbonate and cobalt carbonate are mixed and sintered at 900.degree. C. The resulting LiCoO.sub.2 and lithium are respectively used as a positive electrode active material and a negative electrode in a propylene carbonate electrolyte solution of lithium fluoroborate. In this case, the discharge voltage is about 4 V.
However, when the LiCoO.sub.2 is used, undesired side reactions occur, such as a decomposition of the solvent due to a high charge voltage of 4 V or more (e.g., see Japanese Laid-Open Patent Publication No. 3-49155) or a breakdown of an electrode due to the deintercalation of Li ions (e.g., see U.S. Pat. No. 4,497,726). Because of these side reactions, charge and discharge are conducted only within about one-third of theoretical capacity (assuming a one electron reaction, the theoretical capacity of LiCoO.sub.2 is 274 mAh/g). For example, see Japanese Laid-Open Patent Publication No. 62-90863.